For compressing fluids, such as gas or steam, dry-running reciprocating compressors are especially suitable. As piston sealing elements, piston rings consisting of plastic, for example one-piece piston rings with a straight cut joint or a scarf joint, are preferably used in such reciprocating compressors. One-piece piston rings of this type have the disadvantage that wear of the piston rings which occurs during operation of the reciprocating compressor leads to an enlargement of the distance between the two joint ends of the piston ring, which results in a reduction of the sealing action. Especially during the compression of light gases, such as hydrogen, this enlargement of the joint clearance results in a high leakage at the piston ring already occurring after a relatively short period of operation so that the piston rings already have to be replaced after a relatively short period of operation.
Printed document EP 1275888A1 discloses a piston ring—a so-called twin ring—which is capable of maintaining a certain sealing action even with progressive wear. This twin ring comprises a one-piece sealing ring with a straight cut joint, and comprises a one-piece L-shaped cover ring which covers the sealing ring in the axial and also radial direction. The circumference of the sealing ring and of the cover ring extends in each case over about 340 degrees so that wear compensation is carried out by means of an elastic bending. Such a twin ring has the disadvantage that the sealing action is reduced after a certain time. Moreover, there is the risk that such a twin ring breaks. Moreover, the production costs of such a twin ring are relatively high. Printed document GB129193A and U.S. Pat. No. 1,419,781 each disclose a piston ring. These piston rings have the disadvantage that their installation is difficult, that there is the risk of breakage, that they are relatively expensive to produce, and that they are not suitable for the sealing of high pressures.